How do I scale an angled bone on only two axes?
Select pivot you do not want to move, press Shift + S  Snap Cursor to Selection , press . (Period) key select 3D Cursor the bone will then scale away from the 3D Cursor. Don't forget to press . (Period) and reset to Median Point afterwards.

To see through one bone to another you can toggle Xray in the top right hand corner of the viewport
This will put the bone in the right place, but it will not connect it. To do that, you might be better off not using duplicate (Shift + D ), but rather using extrude (E ), which will branch out a new, connected, parented bone from whatever bone is selected.
I'm not sure what you want here, but if the 3D cursor way is what you need, remember to switch over to the bone tab in the properties editor and change the new bone's parent, probably also checking the box Connected.